Process concepts. Processes. Process in Memory. Process Creation. definition of a process (sometimes called a Task) aprogram in execution

Transcription

1 Processes slide 1 Process concepts slide 2 Silberschatz chapter 3 definition of a process (sometimes called a Task) aprogram in execution an executable file + some kind of dynamic data managed by the OS Process in Memory slide 3 Process Creation slide 4 max parent processes create child processes which, in turn can create other processes stack forming a tree of processes heap data 0 text

2 Unix shell process concepts slide 5 GNU/Linux example slide 6 aprogram or command typed by a user becomes a process when it is run $ gedit foo.txt & the shell is a process shell - parent program or command - child parent may wait or continue after child has started running - use of& Unix shell process commands slide 7 Unix daemon concept slide 8 ps process status abackground process which executes without an associated terminal or login shell top display and update sorted information about processes waits for some event or some specified task on a periodic basis pstree display tree of processes MS Windows equivalents are called services fg,bg,jobs manage foreground, background processes append&to create a process and let the parent continue

3 GNU/Linux Daemon examples slide 9 MS Windows Services slide 10 httpd web server (Apache) see the Windows Task Manager ntpd network time protocol service open up a terminal (cmd) and type the following examples: syslogd system logging to list all the processes yppasswdd TASKLIST /svc to list the processes instantiated from the executable svchost.exe TASKLIST /FI "imagename eq svchost.exe" /svc to list the processes running now: MS Windows Services slide 11 Process States slide 12 TASKLIST /v /fi "STATUS eq running" as a process executes, it changes state: running: instructions are being executed waiting: the process is waiting for some event to occur ready: the process is waiting to be assigned to a processor

4 3State Process Diagram slide 13 Self check question slide 14 new dispatch terminated how could you modify the 3 state process diagram to incorporate partially executed swapped-out processes? ready timeout running I/O completion blocked/ waiting I/O request Process queues slide 15 Context switches slide 16 Job queue: set of all processes in the system Ready queue: set of all processes residing in main memory, ready to execute Device queues: set of processes waiting for an I/O device processes migrate between the various queues when CPU switches to another process, the system must save the state of the old process and load the saved state for the new process the context switch time is overhead; the system does no useful work while switching the information switched from process to process is sometimes called the volatile environment or the register set of the CPU

5 slide 17 How acontext switch is implemented in GNU Luk (comments only) Unix example of Process Creation slide 18 /* *TRANSFER - save the current volatile environment into, * Restore the volatile environment from, p2. */ void SYSTEM_TRANSFER (void **p1, void *p2) { /* * save and disable interrupts * push all registers to the stack * assign p1 = top of stack * assign top of stack = p2 * pop all registers * restore interrupts */ fork system call creates an exact copy ofparent process copied into a new address space - only difference is local pid value exec system call used to replace new process memory space with new program parent can wait or execute concurrently real code consists of assembly language Example fork/exec code slide 19 Example fork/exec code in Python slide 20 #include <stdio.h> #include <stdlib.h> #include <unistd.h> int main () { int pid; /* hold process id in parent. */ pid = fork (); /* create new process. */ /* parent code - wait suspends parent until child finish if (pid > 0) { printf ("parent executing...\n"); wait (0); printf ("parent finished\n"); exit (0); /* child code - exec date. */ if (pid == 0) { printf ("child executing...\n"); execl ("/bin/date", "date", NULL); printf ("execl failed"); exit (1); /* should never get here. */ printf ("fork failed"); exit (1); import os pid = os.fork () if pid > 0: print parent starting... os.wait () print parent finished os._exit (0) if pid == 0: print child starting... os.system ( date ) os._exit (0) print Error if here print fork failed